Different types of plugs and fittings are well known in the art of pressurized vessels and plumbing piping systems such as those used for heating and cooling. Some of these plumbing fittings include valves which are capable of receiving a test probe so that the temperature or pressure within piping or a vessel may be measured. One particular type of device is a valve test plug which includes a valve core of resilient material with an axial seam which receives a measurement probe while maintaining the pressure seal between the interior of the piping of the vessel and the outside environment. An example of such a test plug is disclosed in U.S. Pat. No. 4,926,704 issued to Survil et al.
It is often a requirement of pressurized systems which contain a liquid operating medium that trapped gases such as air be expelled from the system to maintain its normal operation. It is common practice to install air vents at the high points of piping systems and at the top of risers for venting during system filling. Manual air vents should have a non-removable valve stem to prevent accidental removal of the stem under pressure and the top of the stem should be knurled or have a slot for hand or screwdriver operation only. Also, manual air vents should be installed at the high point of the piping system at the top of risers and at all coils.
Furthermore, it is often required to bleed the trapped air or gas prior to taking temperature and pressure measurements. To accomplish this, systems often include a gas bleed valve body which is properly located where trapped air or gas accumulates. Such bleed valves are well known in the art and are used in systems which also include the above-described valve test plug. A problem exists, however, in that the use of separate valve bodies for each of the test and bleed devices adds expense and complexity to a pressurized system such as heating and cooling piping. Furthermore, there are situations in which space is very limited and the manifolds required to support the separate valve bodies which are most often joined by threaded connection to the manifolds occupy too much space in areas of limited access. There is therefore a need for an economical and compact device which provides the combined functionality of a test plug and a gas bleed valve.